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Flickering optos Addams family


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Had a fairly tricky repair yesterday so thought I would document it here... Mainly as a reminder to myself if it ever pops up again.

 

I had very limited tools and spares as I was up in Cairns for work so did this after work to help a guy out that had rung me.

 

1st issue was a coil not firing. When I tested voltage I got 74v at one side of the coil and 71v at the other, though this unusual but also didn't think the coil was an issue. The coil resistance also tested OK and similar to others of the same type. Grounding the tip102 drive transistor didn't fire the coil. Given I had limited tools and parts I thought the easiest way to determine the source of the problem would be to swap the drive wires on the plug from the power driver board with a working coil. The problem stayed with the particular coil, so luckily I had a replacement and swapped it out and all was good. The coil must have had a small break in the winding that was making intermittent contact.

 

2nd issue was a bit more interesting - the thing hand was going up and down a few times and wouldn't drop the ball under the playfield. So I went into thing test and noticed that the thing down opto was flickering really fast.

 

First thing I thought was the opto was dirty, cleaning it made no difference. So then I reseated all the plugs to the small opto thing board, as well as the opto controller board. It worked fine in test mode after that, so I started a game and the same issue reoccurred with thing going up and down multilpe times.... Then went back into thing test and the down opto was flickering again! So I assumed the issue was the opto itself, so sent the owner down to jaycar to get a replacement.

 

While he was gone I kept investigating, pulled the small opto board out a few times (a real pain to remove!) and had a good look at solder connections etc and then decided to put the machine in switch edges rather than thing test. What I then noticed was that it wasn't only the down opto that was flickering, but 2 other switches in that column. However this didn't happen a the time! Sometimes I could lift the playfield and fiddle with plugs around thing and it would test fine.

 

So I went through and tested every switch in the column and they all worked apart from the flickering ones when they were flickering, however when they didn't flicker, they tested fine. Then I decided to closely inspect every switch in that column for a wiring short.

 

What I found was the bookcase open limit switch had a light socket that was only just touching one of the legs of the switch. Moved it away and the problem went away! What I suspect is that when I lifted the playfield, occasionally it would move away slightly and vibration would then get it to short again, making the problem intermittent. By leaving the machine in switch edges while I had a look around and moving wires allowed the owner to watch the display and let me know if the flickering stopped when I moved certain wires or sockets.

 

Sometimes these intermittent ones are really tricky, so hopefully this helps someone! Took me 2.5 hrs to finally track this problem down due to the fact it couldn't be replicated 100% of the time. f6e4edea1da02ec633abe43af0cd38dc.jpg

 

Sent from my ALP-L29 using Tapatalk

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